Refining of oils



Patented June 30, 1936 UNITE STATES PATENT OFFICE REFINING OF OILS No Drawing. Application February 21, 1934, Serial No. 712,412

6 Claims.

This invention relates to improvements in the dewaxing of hydrocarbon oils, more particularly to the dewaxing of petroleum stocks in the manufacture of lubricating oils. The invention provides improved diluents the use of which makes possible improvements in both the economy and the efiiciency of the dewaxing operation.

In conventional dewaxing operations, the stock to be dewaxed is diluted with a diluent such as petroleum naphtha, this stock mixture is chilled to precipitate the wax and the precipitated wax is separated from the chilled stock mixture at low temperature. Recently it has been proposed to use liquid propane, methyl acetate, and blends of benzol and acetone, benzol, acetone and toluol, and benzol and methyl acetate as diluents in such operations.

The improved diluents of this invention comprise the ethyl esters and mixtures of ethyl esters higher boiling than acetic ethyl ester including the valeric ethyl esters, propionic ethyl esters and. butyric ethyl esters. Isovaleric ethyl ester in particular and in general ethyl esters and mixtures of ethyl esters boiling within the range 185-315 F. are particularly advantageous dilucuts.

The improved diluents of this invention have several advantages. Some of these advantages are enjoyed, to some extent, by other diluents hitherto proposed. All of these several advantages are, however, enjoyed in combination by the diluents of this invention.

The ratio of Wax solubility to oil solubility in the diluents of this invention diminishes markedly at low temperatures; that is, the diluents of this invention exhibit a marked selectivity for oil over wax at low temperatures, from 0 F. to F. for example. The diluents of this invention are in this respect superior to most other diluents 4O hitherto proposed; they are in this respect approximately equal to blends of benzol and acetone. This advantage of the diluents of this invention is reflected, in one aspect, by the temperature to which the stock mixture must be chilled to produce a product of given pour test from a given stock. With the diluents of this invention it is possible to produce products of 0 F. pour test from stocks having a viscosity up to about 80 seconds at 210 F. by chilling to about 5 F. and

from stocks of substantially higher viscosity by chilling, for example, to about 20 F. or 30 F.

The diluents of this invention have relatively high solvent capacity for oil at low temperatures as well as at higher temperatures. The diluents of this invention are in this respect superior, for

example, to blends of benzol and acetone. This oil solvent capacity of the diluents of this invention minimizes separation of oil at low temperatures and assists in effecting a sharp separation between oil and wax. 6

The wax precipitated from stock mixtures including the diluents of this invention is in a condition such that it is readily separated from the fluid stock mixture by filtration without requirin more than moderate pressures, and such that 10 it is Well adapted for purification by washing or recrystallization operations. The wax is apparently precipitated from such stock mixtures in a well crystallized condition. This characteristic of the diluents of this invention, in conjunction 15 with their high solvent capacity for oil at low temperature, makes it possible to produce directly wax of relatively high melting point.

The maximum proportions of the diluents of this invention normally required, from 150% to 20 300% by volume on the stock to be dewaxed for example, are moderate, approximating, for example, from 40% to of the volume of blends of benzol and acetone required in comparable instances. 25

The moderate proportions in which the dilucuts of this invention are required, the fact that their characteristics are such that losses can be minimized and the fact that they are available as by-products in the production of ethyl acetate by 30 esterification of acetic acid with alcohol produced by fermentation make them diluents of moderate cost.

The diluents of this invention have no detrimental eifect upon either oil or wax, an advantage 5 also enjoyed, for example, by petroleum naphtha and liquid propane.

The diluents of this invention can be used in conventional apparatus. Special apparatus, high pressure apparatus such as that required for use 40 with liquid propane for example, is not required.

The boiling range of the diluents of this invention corresponds, approximately, to that of the petroleum naphtha conventionally used; the same or corresponding distillation equipment can 45 be used to recover the diluents of this invention from the stock following separation of wax. The diluents of this invention are insoluble in water and can be stripped from lubricating oil mixtures 50 by distillation with steam at temperatures not exceeding 400 F. The relatively high boiling range of the diluents of this invention, 185-315 F. as compared to 132-138 F. for acetone (commercial) and 135 F. for methyl acetate for example, also assists in minimizing losses of the diluent. e V

Because of the relatively high solvent capacity for oil of the .diluents of this invention, they may be used with advantagewithout admixture with other diluents, such as benzoi; for example. Benzol, for example, is conventionally used in diluent blends to increase the solvent capacity of the blend for oil at low temperature because some other component of .the'blend, acetone or methyl acetate for ,example has very littlesolvent capacity for oil at the temperature of wax separation, but benzol also increases the solvent capacity of the blend for wax; The diluents of @this inven' tion are not subject to this limitation. They may, however, be used in conjunction with other diluents'such as benzol, petroleum naphtha or lower boiling hydrocarbons.

The diluents of this invention may be used in blends inclrlding solvents for asphaltic matter, such ascarbon disulphide, toluol, carbon tetrachloride or pyridine. Such blends operate to holdf-natural wax inhibitors in solution throughout ;the dewaxing operation enabling the production of dewaxed stocks which can be givenainishing treatments without increase of the'pour test. s

' 7 Following chilling, the precipitatecl wax is with advantage separated from the fluid stock mix ture including the diluent or diluent mixture of this invention by filtration, in conventional apparatus for example; The separation of precipi- 7 late having" a ,Viscosity of 105 seconds at 100 F. is diluteckwith of its own volume of a mixtated wax may, however, be otherwise efiected. By using high boiling ethylg esters of high spe- ,cific gravity, for example, suspensions of precipitated wax in. fluid stock mixtures can be produced on chilling in which the stock mixture is of higher specific gravity than the precipitated wax. Such suspensions can be separated in the conventional centrifuge even though the wax be definitely crystalline, the precipitated wax floating on and being carried through the centrifuge on the circumambient fiuid stock mixture.

Thefollowing examples of operations embodying the use of diluents of this invention will further illustrate the invention:

Example fl.-A Mid-Continent parafiin distilture of 'ethyi estersboiling within the range 194- 311 F. and consisting essentially of isovaleric I ethyl ester, the mixture is chilled to 0 F., about 23.2% of precipitated wax having a melting point of about 106 F. is separated from the fluid stock mixture by filtration, and the diluent is steam distilled'fro'm the fluid stock mixture, to produce a dewaxed oil having a pour test of 0 F.

TfExctmple 2.A blend of Mid-Continent stocks having. a viscosity of 77 seconds at 210 ,F. is diluted with 300% of its own volume of the same mixture of high boiling ethyl esters? the mixture is chilled to 0 F;, about 10.1% of precipitated wax having a'melting pointof aloout 151? F. is separatedfrom the fluid stock mixture by filtration, and the diluent issteamdistilled from the fluid stock mixture, to produce a; dewaxed oil having a pour test of +6 ,=F.

Example 3.--A biend of Mid-Continent overheadlong residuum having a viscosity of 150 sec-' onds at 210 F. is diluted with 300 of its own volume of the same mixture of high boiling ethyl boilingpoint less than 315 F. r

' F1 EDWARD JOHN MARTIN;

esters, the mixture is chilled to '10 F., about separated. from the fluid stock mixture by filtration, and the diluent is steam distilled from the fluid stocle mixture to produce a dewaxed oil having a pour test of =-5 F.

ErampZe 5.-A Mid-Continent overhead long residuum having a; viscosity of 60 seconds at 210 is diluted with 150% of its own volumei nf the same mixture of high boiling ethyl esters, the Inixtureis chilled to 5 F., about14.6%. precipitated waxhaving a melting point of about F; is separated from the fluic? stock mixture by filtration, and the'diluentis steam distilled from the fluidstock mixture to produce a dewaxed oil having a pour test of 0 F.

' Example 6.-A Pennsylvania" long residuum having a viscosityof 90 seconds at 210 F; and a specific gravity of 0.898 isxiiluted with -300% of its own volume of a mixture of ethyl esters higher boiling than acetic ethyl ester having a specific gravity approximating 0.88-0.89, the mixture ischilled to 15 F; to precipitate wax having a specific gravity of about 0.877, and the precipitated wax is separated from the'fiuid' stock mixture by centriiugingthe fluid stock mixture being separated the centrifuge as theheavy component. r

As used herein,'the term pour test is the lowest temperature at which the .oil will flow when chilled without disturbance, determined; for example, accordance with method D9'7.30 of the'American Society for Testing Materials. Viscosities herein are viscosities in seconds Saybolt universal; i r

*I claim! 7 r g f 1. In the dewaxing of hydrocarbon oils, the improvement which comprises diluting the with a diluent comprising anethyl ester of ajyaleric gem. 7 V V V 2.. In the dewaxing of hydrocarbon oils, the

improvement which comprises diluting the oil with a diluent comprising isovaleric ethyl ester.

3. In the dewaxing of hydrocarbon oils, the improvement which comprises diluting the oil with a diluent comprising abutyric ethyl ester. 4. In the 'dewaxing 0t hydrocarbon oils, the improvement which comprises diluting the oil with a diluent comprisingia mixture of ethyl ese ters higher boiling than acetic' ethyl ester and consisting essentially of isovaleric ethyl ester.

'5. In the dew-axing of hydrocarbon oils, the improvement which comprises diluting the'oil with a diluent comprising a mixture of ethyl esters boiling'witliin the range ?315 F. and

consisting essentially of isovalericethyl ester.

6. In the dewaxing of hydrocarbon oils, the

improvement which comprises diluting the oil with a diluent comprising an ethyl ester' higher boiling than propionic ethyl esterand having a 

